Subsea mining off the West Coast

When the Marsol Pride slipped its moorings in Nelson and headed out to sea at the beginning of March, few people in the town would have realised that a whole new chapter in the history of world gold exploration had just opened. By ALISTAIR MACKENZIE.

The two-month voyage in search of submarine deposits of alluvial gold is the first of several planned around the globe by a marine exploration and mining joint venture between De Beers and AngloGold Ashanti, Africa’s largest producer of bullion.

The exploration also marks a change in thinking by the world’s mining majors who are starting to consider underwater and under-sea mining as increasingly feasible and potentially very lucrative.

The AngloGold Ashanti/De Beers joint venture, formed in October last year, will spend US$40 million over the next three years, and after the West Coast project is established, the JV will investigate various continental shelves around the world.

The Kiwi connection

The West Coast programme was instigated by Dunedin geoscientist Dr John Youngson, whose company Placer Solutions floated the undersea gold project to De Beers. Placer Solutions is working in partnership with exploration company Seafield Resources on the project. Registered in New Zealand, but wholly owned by the South African Oppenheimer mining dynasty (which has a large stake in the De Beers Group), Seafield signed a Memorandum of Understanding with the De Beers/AngloGold Ashanti JV in December last year, providing the JV right to fund and earn an interest in Seafield’s prospecting and exploration activities for at least the next three years (or until the initial funding is exhausted).

Over the course of the programme, the Marsol Pride will drill as many as 400 test holes over a 2000-square-kilometre area of seabed. Seafield’s main permit covers 8689 square kilometers of foreshore and seabed, extending from the low water line to 12 nautical miles offshore, and runs from Karamea in the north to Jackson Bay south of Haast. A separate prospecting license, under the Continental Shelf Act, covers 1490 square kilometres and contains three separate sections, the largest of which runs from north west of Westport to north west of Karamea. The second section lies off Ross and Hokitika with a third off Greymouth.

The resource

Dr Youngson, an internationally recognised authority on placer (alluvial) mineral deposits, believes the glaciers and rivers flowing westwards from the Alps deposited gold bearing sediments on the continental shelf during glacial periods and that these deposits, concentrated into pockets and buried under a blanket of mud and sand, await discovery. Since gold was first discovered on the West Coast in 1864, about 240 tonnes of placer gold have been recovered from West Coast rivers and beaches; but few attempts have been made to locate deposits offshore. Youngson has developed a predictive geological model which he believes will narrow the search considerably.

Exploration

After being awarded a prospecting permit and prospecting license along a 500 kilometre-long strip off the West Coast in 2006, Seafield conducted 4000 line-kilometres of airborne magnetic surveys to identify submerged heavy mineral deposits. The following year, Seafield conducted more than 2483 line-kilometres of shipborne geophysical survey to create a seismic cross-section of the top 200 metres of sediments and detailed bathymetry of the seafloor. The results of both surveys were integrated into the predictive model and a number of submerged shorelines, outwash deposits and post-glacial channels pinpointed.

The test drilling programme was held up for almost 18 months while a sonic vibro-corer sampling drill was developed, tested and modified. The vibrating head on the drill has a hollow core barrel, which allows a continuous 10 metre core of 15cm diameter to be collected. Wellington-based New Zealand Diving & Salvage Ltd (NZDS) helped design the test drill and Nelson-based marine support company Unimar led the construction of the launch and recovery system for the tool. A new buoyancy compensation system was fitted to the drill ship to allow it to rise and fall while keeping the drill stable on sample sites.

Initially small (150mm) cores are being taken to confirm the geophysical details and classify the different geological layers of sediment encountered. Later, larger diameter (300mm) cores will be taken to sample heavy metals present.

The sampling and analysis phase is expected to be complete towards the end of the year.

A seabed mineral rush

Seafield director Grant Stubbs says finding a concentration of one gram of gold per tonne of sediment would be enough to make mining economic. Besides gold, Seafield holds prospecting rights for ilmentite, rutile, platinum group metals, zircon, magnetite, and garnet.

Seafield is just one of several exploration and mining companies to have gained exploration licenses for New Zealand waters in recent years – drawn here not only by the promise of very good returns but also by the country’s stability, infrastructure, and supportive government.

Australia’s Fortescue Metals has applied for about 25,600 square kilometres of exploration and prospecting permits around New Zealand, principally for iron sands. Although the financial crisis has knocked prices recently, the price of iron ore – driven in large part by the demanding Chinese steel industry – has seen suppliers casting around for new deposits, including submarine ones. According to Dr Youngson much of the magnetite (ironsand) found down the West Coast have less impurities from a steelmaking point of view than the titanomagnetite ironsand used by New Zealand Steel for its Waiuku plant.

But it’s the deep offshore waters of New Zealand (and other Pacific nations) that hold the interest of two of the largest players in submarine mining. Canadian registered Nautilus Minerals holds more than 370,000 square kilometres of tenement licenses and exploration applications in the territorial waters of PNG, Fiji, Tonga, the Solomon Islands, and New Zealand. Australian-based Neptune Minerals has exploration licenses covering more than 278,000 square kilometres in the territorial waters of New Zealand, PNG, the Federated States of Micronesia, and Vanuatu. In 2008, Neptune applied for a mining license for two deposits in about 1250 metres of water near the Kermadec Islands. The company has exploration rights over 35,000 square kilometres of New Zealand waters.

Methodology

The advent of satellite navigation systems and technological advances by the offshore oil and gas industry have made submarine mining increasingly feasible.

Deep-water pumps and suction pipes developed to bring subsea oil up to the surface could be used by miners to drag minerals (mixed with water) to the surface through riser pipes from a massive-sulphide mine.

Remotely-operated vehicles used to make trenches for seabed pipelines could be adapted to cutting ore. Depth is less of a barrier than it was: Woods Hole Oceanographic Institution has a vehicle that can reach depths of 11 kilometres.

Conservation

Perhaps more challenging, will be the environmental aspects of subsea mining, which is an acutely sensitive issue.

De Beers is quick to point out it has been mining on the Atlantic shelf off southern Africa for almost 20 years without adverse affect on the environment and with regular internal and independent monitoring.

A De Beers spokesman said independent studies by marine scientists have been commissioned there and in New Zealand to ensure that potential effects of activities are known and “that actual effects on indigeneous flora and fauna are insignificant and minimised.”

The De Beers and AngloGold Ashanti environmental management systems are accredited to International Standard ISO14001.

Nevertheless, mining and exploration in shallower coastal waters will undoubtedly meet stiff opposition. The Green Party has already come out strongly against mining off the West Coast because of the potential for environmental damage.

Some opponents to subsea mining in New Zealand fear prospecting, particularly by large players like AngloGold Ashanti and De Beers, will create a momentum of its own and mining may be allowed as a matter of course.

The world’s mining industry is doubtless paying close attention to developments in New Zealand and not far from the front of their minds will be the saga of Nautilus Minerals’ US$310 million Solwara 1 mining project. Involving over 186,000 square kilometres of seabed under Papua New Guinea’s territorial waters and containing an estimated 60,000-100,000 tonnes of copper (along with some gold) the operation was due to start production next year, but is now on hold due to local opposition.

Mining the Deep Sea: what’s it worth?

By Southern Fried Scientist, on December 13th, 2011

The shimmering insides of a vent chimney

In Jules Verne’s 20,000 Leagues Under the Sea*, the iconic Captain Nemo announced that “in the depths of the ocean, there are mines of zinc, iron, silver and gold that would be quite easy to exploit” while predicting that the abundance of marine resources could satisfy human need. If the pace of development for deep-sea mining projects and the estimated value of deep-sea ores is any indicator, it seems as though our misanthropic mariner was wrong on both counts.

In The abundance of seafloor massive sulfide deposits, an international team of geologists attempts to quantify the total available copper and zinc contained in deep-sea massive sulfide mounds. Seafloor massive sulfide mounds are a byproduct of the processes that create deep-sea hydrothermal vents. As super-heated sea water emerges from the vent, it deposits heavy metals and other elements and minerals along the walls of the vent. Over thousands of years, an active vent field can build up a huge mound of metal and mineral rich ore – a massive sulfide mound. In addition to copper and zinc, these mounds can contain gold and silver. Generally, the ore is of much higher quality than its terrestrial counterpart. Over the last few decades, many exploration companies were eyeing these deposits, but it’s only recently that technological developments and economic incentives have aligned to permit potentially profitable deep-sea mining.

Not all hydrothermal vent systems produce massive sulfide mounds, and not all massive sulfide mounds are rich in heavy metals and valuable ore. To determine how much ore really is available in the deep sea, Hannington and his team examined 32 control sites of approximately equal size that broadly represent the geologic conditions of the global seafloor. They discovered 106 ore deposits great than 100 square meters, with many concentrated around neo-volcanic regions (areas of volcanic activity where most hydrothermal vents are found). Based on these samples, they estimated that there are approximately 900 neo-volcanic massive sulfide deposits, but that number could be as low as 500 or as high as 5000.

Determining how many deposits exists is the easy part, figuring how much ore they actually contain is much harder. Using drilling data from the most well-studied of these deposits, they attempted to estimate the tonnage of copper and zinc. From 62 well-studied sulfide deposits, they extrapolated out to total available copper and zinc contained within neo-volcanic seafloor massive sulfides. Obviously, the total tonnage is an estimate with wide error bars, biased by, among other issues, the fact that the most well-studied sulfide deposits also tend to be the largest. As a baseline, they provide a solid preliminary estimate of the amount of available ore locked up in massive sulfide mounds.

From the assumption that there are approximately 1000 deposits greater than 100 tons, and based on previously determined size distributions, it appears as though the total amount of ore in neo-volcanic massive sulfides is on the order of 600,000,000 tons, with 400,000,000 contained in the largest 10% of deposits. From there, they estimate that the total copper and zinc contained in that ore is approximately 30,000,000 tons.

While the potential payouts for deep sea mines is still large, it is not nearly as enormous as previously predicted. This is good news for the creatures that live at hydrothermal vents, as it means that the oft-predicted gold rush of deep-sea mining companies racing to exploit the ocean will be more of a trickle, with fewer companies likely targeting only the largest sulfide deposits. The fact that a third of the mineral wealth is contained in only 10% of deposits means that mining efforts will be more spread out, limiting the impact on any one region.

This is not entirely good news though. While I loath the idea of deep-sea mining, it is impossible not to draw comparisons between deep sea and terrestrial mines. In terms of human impacts and environmental destruction, terrestrial mining has one of the worst track records of any industry (see Amy’s article here). In contrast, deep-sea mining, as an emergent industry, has the potential to act as a responsible environmental steward, setting a high bar for monitoring, mitigation, and conservation (see Rumors from the Abyss here). The dynamic nature of hydrothermal vent ecosystems means that they are much more resilient to environmental disturbance than their terrestrial counterparts. The relatively low value of massive sulfide deposits means that we are stuck with terrestrial mining, and its history of exploitation and environmental degradation, for a long time.